Effect of cell culture medium components on color of formulated monoclonal antibody drug substance.

As the industry moves toward subcutaneous delivery as a preferred route of drug administration, high drug substance concentrations are becoming the norm for monoclonal antibodies. At such high concentrations, the drug substance may display a more intense color than at the historically lower concentrations. The effect of process conditions and/or changes on color is more readily observed in the higher color, high concentration formulations. Since color is a product quality attribute that needs to be controlled, it is useful to study the impact of process conditions and/or modifications on color. This manuscript summarizes cell culture experiments and reports on findings regarding the effect of various media components that contribute to drug substance color for a specific monoclonal antibody. In this work, lower drug substance color was achieved via optimization of the cell culture medium. Specifically, lowering the concentrations of B-vitamins in the cell culture medium has the effect of reducing color intensity by as much as 25%. In addition, decreasing concentration of iron was also directly correlated color intensity decrease of as much as 37%. It was also shown that the color of the drug substance directly correlates with increased acidic variants, especially when increased iron levels cause increased color. Potential mechanisms that could lead to antibody coloration are briefly discussed.

Crystalline protein domains and lipid bilayer vesicle shape transformations.

Cellular membranes can take on a variety of shapes to assist biological processes including endocytosis. Membrane-associated protein domains provide a possible mechanism for determining membrane curvature. We study the effect of tethered streptavidin protein crystals on the curvature of giant unilamellar vesicles (GUVs) using confocal, fluorescence, and differential interference contrast microscopy. Above a critical protein concentration, streptavidin domains align and percolate as they form, deforming GUVs into prolate spheroidal shapes in a size-dependent fashion. We propose a mechanism for this shape transformation based on domain growth and jamming. Osmotic deflation of streptavidin-coated GUVs reveals that the relatively rigid streptavidin protein domains resist membrane bending. Moreover, in contrast to highly curved protein domains that facilitate membrane budding, the relatively flat streptavidin domains prevent membrane budding under high osmotic stress. Thus, crystalline streptavidin domains are shown to have a stabilizing effect on lipid membranes. Our study gives insight into the mechanism for protein-mediated stabilization of cellular membranes.